The TRRL has carried out a number of investigations to assess the fatigue performance of welded joints in orthotropic bridge decks. The assessment method is based on the UK design code, BS 5400 part 10. Stresses due to traffic loading were obtained from static load tests on trial deck panels in the laboratory under a single wheel load, and on bridges using a two axle test vehicle. This report describes constant amplitude fatigue tests carried out on some of the main types of welded joint in two designs of deck panel used on bridges in the UK and elsewhere. The test results were used to assign the joints to the appropriate weld class in the design code. The joints tested were: the longitudinal stiffener (trough) to deck; alternative types of trough to crossbeam; trough splice; crossbeam to deck; longitudinal web to deck; and deck plate butt welds. For most joints the test specimen and loading were designed to simulate the passage of single wheels over the joint and fatigue strength can be expressed in terms of stress in the plate adjacent to the weld. It was found that several of the joints could be upgraded compared to the BS 5400 classifications, but inspection and quality assurance requirements are likely to limit the weld class which can be used for joints on bridges.